检查 localStorage 中的值是否大于先前的值

Question

I am setting an item in localStorage

{typeof window.== 'undefined' && localStorage,setItem('userData'. topic.progress)}

and then I want to check to see if the value is greater than or less than the previous value, only values greater than should then be set.

However currently it is always changing to the progress value even if the value is lower

my data looks like this:

{
topic1: { progress: '20'},
topic2: {progress: '25'},
topic3: {progress: '30'}
}


let progress = ''

  if (localStorage.getItem('userData') !== null && localStorage.getItem('userData') > progress) {
    progress = localStorage.getItem('userData')
  } else if (localStorage.getItem('userData') < progress) {
    console.log('less than')
  }

Answer 1

The value returned by localStorage.getItem() is always a string.
You need to convert the value to a number , eg:

const numericLS = parseInt( localStorage.getItem('userData'), 10 );

Changing the data type to string everywhere does not help, because string comparison compares character-by-character, not by the numeric value, eg:

"9" < "89" // false
"9" < "90" // true

Example:

localStorage.setItem('userData', 25);

var progressValues = [ 2, 3, 20, 25, 200, 30 ]; // <--- use numeric values

progressValues.forEach( function( progress ){
  const LS = localStorage.getItem('userData');

  const numericLS = parseInt( LS, 10 );  // <--- convert to number

  if( numericLS < progress ){
    console.log('set larger', progress, ', was', numericLS);
    localStorage.setItem('userData', progress);
  } else {
    console.log('skip smaller', progress, ', keep', numericLS);
  }
})